Projector

ABSTRACT

To provide a thin projector, such as a rear projector, formed by a less expensive projection optical system which is easy to assemble and install, and performing a highly accurate projection, projection light PL projected with a projection optical system onto a screen is linearly polarized light having a polarization azimuth along the longitudinal direction of the screen. With this arrangement, the right and left ends of the rear surface of the screen maintain a low reflectance, thereby reducing a loss in quantity of illumination light when passing through the screen, in other words, achieving high luminance of an image projected onto the screen while maintaining its uniformity of brightness.

This is a Continuation of application Ser. No. 10/805,241 filed Mar. 22,2004. The entire disclosure of the prior application is herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a projector projecting an image byusing spatial light modulation devices, such as liquid crystal panels.

Among related art rear projection projectors, a shallow rear projectoris prevailing, in which image light emitted from a projection opticalsystem disposed behind and at the lower part of a screen is eventuallyreflected toward the forward direction, while being reflected at atleast one plane mirror to secure a light path, so as to be projectedonto the screen See Japanese Unexamined Patent Application PublicationNo. 5-66482.

A projection display apparatus in which a diagonal projection having alarge magnification is possible by forming its projection optical systemwith a plurality of concave and convex mirrors having different opticalaxes from each other has been proposed. See Japanese Unexamined PatentApplication Publication No. 2001-255462. The projection displayapparatus has a thin structure by achieving a high magnification and adiagonal projection.

SUMMARY OF THE INVENTION

According to the former method using the plane mirror, although the rearprojector has a relatively thin structure, distortion occurs and theprojector becomes taller. Also, not only the relatively large planemirror makes the projector heavier but also the plane mirrorincorporated in an actual projector, requires a special mechanism toadjust displacements of the projection optical system and the planemirror, thereby increasing an adjusting step and resultantly a cost ofthe projector.

Also, according to the latter method, using the projection opticalsystem formed by a plurality of concave and convex mirrors, although theprojection display apparatus can project a relatively highly accurateimage while maintaining a thin structure, and adjusting work in the caseof incorporating a plane mirror can be eliminated, the projectionoptical system itself is hard to assemble and adjust, thereby resultingin an increased cost of the projection display apparatus.

In view of the above problems, the present invention provides a thinprojector (projection apparatus), such as a rear projector, formed by aless expensive projection optical system which is easy to assemble andinstall, and performs highly accurate projection.

In order to address the above problems, a projector according to anaspect of the present invention includes an illumination device to emitillumination light; spatial light modulation devices illuminated withillumination light emitted from the illumination device; a projectionoptical system to project image light emitted from the spatial lightmodulation devices; a flat and rectangular screen onto which the imagelight passing through the projection optical system is projected; and apolarizing device to make the image light emitted from the spatial lightmodulation devices incident on the screen so as to serve as linearlypolarized light having a polarization azimuth along a predetermineddirection except for the lateral direction of the screen. Here, the term“spatial light modulation device” refers to an optical devicerepresented by, for example, a liquid-crystal light valve, and has anembodiment including a digital mirror device.

In this projector, since the polarizing device makes the image light,emitted from the spatial light modulation devices, incident on thescreen, so as to serve as linearly polarized light having a polarizationazimuth along a predetermined direction, except for the lateraldirection of the screen, the longitudinal both ends of the screen canalso maintain a low reflectance, thereby reducing a loss in quantity ofimage light when passing through the screen. Accordingly, even when thisstructure is applied to, for example, a thin rear projection typeprojector having a large projection magnification, high luminance of animage can be achieved while maintaining the uniformity of brightnessacross the entire screen.

In a specific modification of the projector, the polarizing device makesthe image light emitted from the spatial light modulation devicesincident on the screen so as to serve as linearly polarized light havinga polarization azimuth along the longitudinal direction of the screen.In this case, a loss in quantity of illumination light incident on thelongitudinal both ends of the screen can be minimized, thereby providinga projector exhibiting relatively less unevenness of brightness as awhole.

Also, in a specific variation of the projector, the screen is a rearprojection screen including a Fresnel lens portion disposed at theincident side thereof and a diffusing screen portion, such as alenticular lens, disposed at the exit side thereof. Meanwhile, TheFresnel lens portion has a flat incident surface. In this case, areflection loss of both ends of the flat incident surface having a largeincident angle from the projection optical system to the flat incidentsurface of the Fresnel lens can be reduced.

In addition, in another specific variation of the projector, thepolarizing device includes polarization filters disposed at the exitsides of the corresponding spatial light modulation devices. In thiscase, the projector has a simple structure having only the polarizationfilters disposed at the exit sides of the spatial light modulationdevices. When the spatial light modulation devices are liquid-crystallight valves, although the polarization filters are disposed at theincident and exit surfaces of each liquid-crystal light valve, thepolarization filters at the corresponding exit sides are disposed incorresponding predetermined azimuths so as to serve as the polarizingmeans. Also each polarization filter at the incident side is disposedsuch that its azimuth is turned by, for example, 90 degrees with respectto that of the corresponding polarization filter at the exit side.

Furthermore, in another specific variation of the projector, theprojection optical system includes an L-shaped optical unit to bend alight path, having a pair of lens groups and reflecting deviceinterposed therebetween. In this case, the projection optical system hasa reduced length extending in the optical axis direction on the exitside of the optical unit, and also, optical components, such as theillumination device can be disposed at lateral sides of the opticalunit. Thus, a projector or the like having, for example, a rearprojection screen housed therein does not require a relatively largereflecting mirror or the like, substantially opposed to the screen to beincorporated in its housing. As a result, a shallow and thin projectorcan be achieved in spite of the fact that it is light and is easy toassemble and manufacture. Meanwhile, the L-shaped optical unit has asimple structure in which a reflecting device, such as a mirror, ismerely incorporated therein while known lens systems being basicallyused, thereby making an optical design and manufacturing of theprojector easy.

Also, another projector according to an aspect of the present inventionincludes an illumination device to emit illumination light; spatiallight modulation devices illuminated with illumination light emittedfrom the illumination device; a projection optical system which includesan L-shaped optical unit to bend a light path, having a pair of lensgroups and a reflecting device interposed therebetween and whichprojects image light emitted from the spatial light modulation devicesvia the optical unit; and a screen onto which the image light passingthrough the projection optical system is projected.

In this projector, since the projection optical system projects imagelight emitted from the spatial light modulation devices via the L-shapedoptical unit to bend a light path, having the pair of lens groups andthe reflecting device interposed therebetween, the projection opticalsystem has a reduced length extending in the optical axis direction onthe exit side of the optical unit. Also optical components, such as theillumination device, can be disposed at lateral sides of the opticalunit. Thus, a shallow and thin projector can be achieved. Meanwhile, anoptical design of the L-shaped optical unit is simple.

Also, in a specific variation of the projector, the screen is a rearprojection screen, and the optical unit directly focuses the image lightemitted from the spatial light modulation devices onto the screen. Inthis case, since the projector has a structure in which a relativelylarge reflecting mirror substantially opposed to the screen is notincorporated in the housing thereof, a thin projector can be achieved inspite of the fact that it is light and is easy to assemble andmanufacture.

In addition, in another specific variation of the projector, the opticalunit has an optical axis bent on a vertically extending plane orthogonalto the screen. In this case, optical components, such as theillumination device can be reliably disposed around an upper part and/ora lower part of a plane orthogonal to the optical axis direction, andalso the structure of the optical unit can be simple.

Furthermore, in another specific variation of the projector, theillumination device is disposed such that the optical axis of a lampserving as a light source to generate illumination light lieshorizontally. In this case, an operation of the lamp can be stabilized.

Still furthermore, in another specific variation of the projector, theexit-side optical axis of the projection optical system is perpendicularto a surface of the screen extending along the central part of thescreen. In this case, an image projected by the projection opticalsystem onto the screen has less aberration, such as distortion.

Moreover, in another specific variation of the projector, there areprovided a color modulation device including the spatial lightmodulation devices for a plurality of colors, for corresponding colors,each device being illuminated with corresponding illumination lightemitted from the illumination device, and a light-separation modulationdevice which includes a light-synthesizing member to synthesizecorresponding kinds of color image light emitted from the colormodulation device and which emits the synthesized image light. Theprojection optical system projects the image light synthesized with thelight-synthesizing member onto the screen. In this case, a color imagehaving a highly uniform luminance can be projected by a shallow and thinprojector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a projector according to an exemplaryembodiment of the present invention;

FIGS. 2(a) and 2(b) are schematics of the projector;

FIG. 3 is a sectional schematic of a screen;

FIG. 4 is a schematic illustrating the structure of an optical systemportion;

FIG. 5 is a schematic illustrating the structure of a projection opticalsystem;

FIG. 6 is a graph illustrating light extinction due to the screen;

FIG. 7 is a graph illustrating light extinction due to another screen;and

FIG. 8 is an illustration of areas on the screen.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The structure of a projector according to an exemplary embodiment of thepresent invention will be described with reference to the accompanyingdrawings.

FIG. 1 illustrates the projector according to an exemplary embodiment,that is, an elevation view of the projector, and FIGS. 2(a) and 2(b) arerespectively a perspective plan view and a perspective side view of theprojector.

A projector 10 has a structure in which a main body formed by an opticalsystem portion, an electrical circuit, and so forth is accommodated andheld in a casing 12 serving as a housing.

The casing 12 has a screen 14 fixed across the entire front surfacethereof in an embedded state. The screen 14 is a rear projection screenilluminated with projection light emitted from the inside of the casing12 and has a rectangular shape which has a long width relative to thelength. That is, which extends longer in the horizontal direction thanin the vertical direction.

FIG. 3 is an illustration of the sectional structure of the screen 14.The screen 14 has a triple layer structure formed by a transparentsubstrate 14 a, a screen film 14 b, and a Fresnel lens 14 c laminated inthat order. The transparent substrate 14 a is made from a transparentparallel plate and has the screen film 14 b bonded and closely contactedto the rear surface thereof. The screen film 14 b is also referred to asa lenticular screen and has a large number of microlenses formed on thesurface thereof opposed to the Fresnel lens 14 c. The shape, the size,the arrangement, and the like of the microlenses are appropriatelydecided taking the use of the projector, the compatibility with otheroptical systems, and so forth into account.

The Fresnel lens 14 c is fixed to the transparent substrate 14 a with afixing member (not shown) in a state in which it is opposed to thescreen film 14 b, having a gap GA interposed therebetween. The Fresnellens 14 c has a flat surface 14 f formed on the incident side thereofand lens protrusions 14 g, each having a ring belt shape, formed on theexit side thereof. Projection light PL incident on the rear surface ofthe Fresnel lens 14 c is converted into a flux substantiallyperpendicular to the screen 14 with the Fresnel lens 14 c and isincident on the screen film 14 b. The projection light PL incident onthe screen film 14 b, serving as image light, is scattered atappropriately distributed angles with the screen film 14 b and istransmitted through the transparent substrate 14 a.

Referring back to FIGS. 1 and 2, behind the screen 14 and in the casing12, the projector 10 includes an illumination device 21 including alight source to generate illumination light, a color-separationmodulation optical-system 23 to form a transmittance distributioncorresponding to an image by applying spatial light modulation onillumination light emitted from the illumination device 21 and aprojection optical system 25 to project the transmittance distributionformed with the color-separation modulation optical-system 23 onto thescreen 14 with an appropriate magnification. An optical system portionincluding the illumination device 21, the color-separation modulationoptical-system 23 and the projection optical system 25 is constructedsuch that these components are reliably fixed in the casing 12 withrespective retaining members (not shown) and that the positionalrelationship and the like among them can be finely adjusted if needed.

The projection light PL projected with the projection optical system 25onto the screen 14 is linearly polarized light having a polarizationazimuth along the longitudinal direction of the screen 14. With thisarrangement, as will be described later, the right and left ends of therear surface of the screen 14 also maintain a low reflectance, therebyreducing a loss in quantity of projection light when passing through thescreen, specifically, achieving high luminance of an image projectedonto the screen 14 while maintaining its uniformity of brightness.

Also, an exit-side optical axis OA1 of the projection optical system 25perpendicularly intersects with the plane of the screen 14 extendingalong the central part of, that is, the center of the screen 14. Withthis arrangement, an image projected with the projection optical system25 onto the screen 14 becomes highly accurate and sharp with lessaberration, such as distortion.

Also, the projection optical system 25 is an L-shaped optical unit, andan incident-side optical axis OA2 thereof is perpendicular to theexit-side optical axis OA1 and extends downwards in the verticaldirection. Image light emitted from the projection optical system 25 isdirectly incident on the screen 14 without passing through an opticalmember, such as a mirror. With this arrangement, the optical systemportion, including the illumination device 21 and the color-separationmodulation optical-system 23, can be arranged in directionsperpendicular to the optical axis OA1 with respect to the projectionoptical system 25, that is, in a surrounding space extending. Forexample, downwards and sidewards from the projection optical system 25but not rearwards from the projection optical system 25. The size of theoptical system portion including the illumination device 21, thecolor-separation modulation optical-system 23 and the projection opticalsystem 25 can be made shorter in the direction along the optical axisOA1, thereby achieving a relatively thin projector without using a planemirror to secure a light path. Also, since no mirror is needed to beincorporated in the housing, distortion or displacement of an imagecaused by the mirror inserted in the light path can be reduced orprevented. As a result, a correction mechanism and a correction stepagainst these problems can be eliminated. In addition, since the mirrorand a mechanism accompanying the mirror can be eliminated, a shallow andthin projector can be achieved in spite of the fact that it is light andis easy to assemble and manufacture.

FIG. 4 is an elevation view illustrating the structure of the opticalsystem portion including the illumination device 21, thecolor-separation modulation optical-system 23 and the projection opticalsystem 25. FIG. 5 is a side view illustrating the structure of theprojection optical system 25.

The illumination device 21 includes a light source lamp 41, a firstfly-eye lens 43, a second fly-eye lens 45, a polarization-conversingmember 47, and a superimposing lens 49. Here, an example of the lightsource lamp 41 is a high-pressure mercury-vapor lamp including a concavemirror for collimating source light. Also, the first fly-eye lens 43,having a plurality of element lenses arranged in a matrix pattern,divides the source light emitted from the light source lamp 41 andseparately collects it with these element lenses. The second fly-eyelens 45, also having a plurality of element lenses arranged in a matrixpattern, forms uniform divergent light from secondary light sourcesformed with the first fly-eye lens 43 and emits uniform illuminationlight to be superimposed on light valves (spatial light modulationdevices), which will be described later, with these element lenses. Thepolarization-conversing member 47 converts the illumination lightemitted from the second fly-eye lens 45 into only a polarized componentorthogonal to the plane of FIG. 4 and supplies it to the followingoptical system. The superimposing lens 49 converges the illuminationlight passing through the polarization-conversing member 47 if needed sothat the light valves in the color-separation modulation optical-system23 can perform superimposing illumination. An optical axis OA3 of theillumination device 21 extends horizontally, and resultantly, the lightaxis of the light source lamp 41 also extends horizontally. As a result,the light source lamp 41 lies horizontally, whereby stable lightemission can be achieved by maintaining an operating temperature and thelike of the light source lamp 41 in a stable state and also the lifespan of the light source lamp 41 can be extended.

The color-separation modulation optical-system 23, serving as alight-separation modulation device, includes first and second dichroicmirrors 51 and 52, three field lenses 53 a to 53 c, three light valves54 a to 54 c, a cross dichroic prism 55, three pairs of polarizationfilters 56 a to 56 c arranged so as to sandwich the corresponding lightvalves 54 a to 54 c. Among them, the light valves 54 a to 54 c and thepolarization filters 56 a to 56 c form a color modulation device. Bluelight (B light) reflected at the first dichroic mirror 51 is reflectedat a reflecting mirror M1, passes through the field lens 53 a, and isincident on the light valve 54 a sandwiched between the pair ofpolarization filters 56 a. Green light (G light), transmitted throughthe first dichroic mirror 51 and reflected at the second dichroic mirror52, passes through the field lens 53 b and is incident on the lightvalve 54 b sandwiched between the pair of polarization filters 56 b. Redlight (R light), transmitted through the first and second dichroicmirrors 51 and 52, passes through a relay lens R1, is reflected at areflecting mirror M2, passes through a relay lens R2, is reflected at areflecting mirror M3, passes through the field lens 53 c and is thenincident on the light valve 54 c sandwiched between the pair ofpolarization filters 56 c. Each of the light valves 54 a to 54 c serveas a spatial light modulation device to modulate the correspondingspatial intensity distribution of illumination light incident thereon.The three kinds of color light, incident on the corresponding lightvalves 54 a to 54 c, are respectively modulated thereby, are synthesizedwith the cross dichroic prism 55 serving as a light-synthesizing memberand are then emitted from a side surface thereof. The synthesized light,emitted from the cross dichroic prism 55, is incident on the projectionoptical system 25.

The projection optical system 25 is formed by a front first lens group25 a, a prism mirror 25 b to bend a light path and a rear second lensgroup 25 c. Here, the first lens group 25 a is composed of six concaveand convex lens elements. Also, the second lens group 25 c is composedof three meniscus lens elements. The prism mirror 25 b, sandwichedbetween the two lens groups 25 a and 25 c, serves as a reflecting deviceso as to bend a vertical light path by 90 degrees into a horizontallight path. The exit-side optical axis OA1 and the incident-side opticalaxis OA2 of the projection optical system 25 are perpendicular to eachother on the reflective surface of the prism mirror 25 b.

An operation of the projector according to the exemplary embodimentshown in FIGS. 1 to 5 will be described. The illumination device 21serves as a white light source generating the three kinds of R, G, and Blight. Illumination light, emitted from the illumination device 21,undergoes color separation with the dichroic mirrors 51 and 52 disposedin the color-separation modulation optical-system 23 and the three kindsof separated color light are incident on the corresponding light valves54 a to 54 c. Each of the light valves 54 a to 54 c, modulated inaccordance with an external image signal, has a two-dimensionalrefractive-index distribution and modulates the illumination lightincident thereon. The three kinds of illumination light, that is, imagelight modulated with the light valves 54 a to 54 c, as mentioned above,are synthesized with the cross dichroic prism 55 and the synthesizedimage light is incident on the projection optical system 25. The imagelight, incident on the projection optical system 25, is incident on thescreen 14 so as to serve as linearly polarized light having apolarization direction along the longitudinal direction of the screen14. In this case, the polarization direction of projection light is setin the longitudinal direction of the screen 14, thereby achieving highluminance of an image projected onto the screen 14 while maintaining itsuniformity of brightness.

Each of FIGS. 6 and 7 is a graph illustrating, by simulation, therelationship between polarization direction of image light.Specifically, the projection light PL incident on the screen 14 disposedin the projector 10 shown in FIG. 1 and the other related figures andrelative light intensity, that is, light extinction rate of an imagelight when passing through the screen 14. In these graphs, thehorizontal and vertical axes represent a projection magnification and arelative light intensity, respectively.

Here, the term “projection magnification” refers to the ratio H/WD,where H represents the diagonal length of the screen 14 and WDrepresents the projection distance from the projection optical system 25to the screen 14, and the greater the projection magnification, thegreater the divergent angle of image light becomes. Also, the term“relative light intensity” refers to the ratio of the quantity of lighttransmitted through the screen 14 to that of light incident on the same.As the relative light intensity, a transmittance is computed inaccordance with the Fresnel reflection formula, taking an incident angleand a perpendicularly polarized component of the image light incident onthe screen 14 as parameters. The graphs shown in FIGS. 6 and 7respectively correspond to the cases of using the screen 14 having anaspect ratio of 9 to 16, that is, having long width relative to thelength, and the screen 14 having an aspect ratio of 3 to 4.

FIG. 8 illustrates areas on the screen 14, the relative lightintensities of which are compared to each other between FIGS. 6 and 7.The center, each of the right and left ends, each of the upper and lowerends, and each of the corners of the screen 14 are respectively definedas a central area CA, a horizontal end area HEA, a vertical end areaVEA, and a diagonal end area DEA. With reference to these areas, marksshown in FIGS. 6 and 7 will be described. Each of the solid and opensquare marks represents a light extinction rate of linearly polarizedlight incident on the horizontal end areas HEA, each of the solid andopen round marks represents a light extinction rate of linearlypolarized light incident on the diagonal end areas DEA, and each of thesolid and open diamond marks represents a light extinction rate oflinearly polarized light incident on the vertical end areas HEA. Each ofthe straight lines in FIGS. 6 and 7, which exhibits a relative lightintensity of about 0.87 and does not vary, represents a light extinctionrate of linearly polarized light incident on the central area CA.

Also, each of the solid square, round, and diamond marks represents alight extinction rate in the case where image light incident on thescreen 14 is linearly polarized light polarized in the longitudinaldirection, that is, in the horizontal direction, corresponding to thepolarization direction of the image light in the projector according tothe present exemplary embodiment. Each of the open square, round, anddiamond marks represents a light extinction rate in the case where imagelight incident on the screen 14 is linearly polarized light polarized inthe lateral direction, that is, in the vertical direction, correspondingto the polarization direction of the image light in a comparativeexample projector.

As shown in both graphs, in the horizontal end areas HEA and thediagonal end areas DEA, a reflection loss of polarized light in thehorizontal direction due to the screen 14 is less than that in thevertical directionThe reflection loss of polarized light in the verticaldirection due to the screen 14 is very large. Also, in the vertical endareas VEA, a reflection loss of polarized light in the verticaldirection due to the screen 14 is less than that in the horizontaldirection. Even in the case of polarized light in the horizontaldirection, a loss due to the screen 14 does not increase so much. Insummary, when the entire screen 14 is intended to be uniformlyilluminated, by setting the polarization direction of image light in thelongitudinal direction of the screen 14, the image light is unlikely tosuffer from bias in accordance with the Fresnel reflection formula.Although a transmittance in the vertical end areas VEA is somewhatsacrificed, transmittances in the horizontal end areas HEA and thediagonal end areas DEA become relatively higher, whereby projectionlight having a uniform distribution as a whole is incident on thescreen.

In addition, this phenomenon becomes significant as the projectionmagnification becomes greater. Accordingly, in the projector 10 offeringa greater projection magnification that is, in the projector 10 of adirect projection type in which no mirror to bend a light path isdisposed between the projection optical system 25 and the screen 14, itis very important to convert image light into polarized light in thehorizontal direction as in the present exemplary embodiment from theviewpoint of achieving uniform illumination of the screen 14. Also, theabove arrangement is very important to achieve a magnified size of thescreen and a thin structure of the projector at the same time.

Although the present invention has been described according to anexemplary embodiment, it is not limited to the foregoing exemplaryembodiment. For example, when the screen 14 has long length relative tothe width, image light to be incident on the screen 14 is converted intolinearly polarized light in the vertical direction, that is, as in itslongitudinal direction.

Also, image light to be incident on the screen 14 can be converted intolinearly polarized light not only in its longitudinal direction but alsoin its diagonal direction. In other words, linearly polarized light inthe lateral direction of the screen 14 may be contained as long as it isnot dominant.

In addition, a polarizing device to make linearly polarized light in adesired direction incident on the screen 14 is not limited to the threepairs of the polarization filters 56 a to 56 c, each pair sandwichingthe corresponding light valves 54 a to 54 c. But it may be speciallyformed irrelevantly to the light valves 54 a to 54 c. In addition, thepolarization filters 56 a to 56 c disposed on the exit sides of thecorresponding light valves 54 a to 54 c may be single one commonlyformed on the exit surface of the cross dichroic prism 55.

Furthermore, although the exit-side optical axis OA1 and theincident-side optical axis OA2 of the projection optical system 25 areperpendicular to each other in the foregoing exemplary embodiment, thedegree of bend between the optical axes of the first lens group 25 a andthe second lens group 25 c may be changed in accordance with theapplication and/or the purpose of the projector if needed.

Still furthermore, although the exit-side optical axis OA1 of theprojection optical system 25 is orthogonal to the central part of thescreen 14 in the foregoing exemplary embodiment, the optical axis OA1may be slightly slanted with respect to a line perpendicular to thescreen 14.

Moreover, although the screen 14 is formed by the transparent substrate14 a, the screen film 14 b, and the Fresnel lens 14 c in the foregoingexemplary embodiment, the screen is not limited to this structure andmay have another optical element incorporated therein. In this case, bymaking divergent image light incident on a surface so as cause thepolarization direction of the image light to agree with the longitudinaldirection of the screen 14, the phenomenon of a reduced transmittance atlongitudinal both ends of the screen can be reduced or prevented.

1. A projector, comprising: an illumination device to emit illuminationlight; spatial light modulation devices illuminated with illuminationlight emitted from the illumination device; a projection optical systemincluding an L-shaped optical unit to bend a light path, having a pairof lens groups and reflecting device interposed therebetween and whichprojects image light emitted from the spatial light modulation devicesvia the optical unit; and a screen onto which the image light passingthrough the projection optical system is projected.
 2. The projectoraccording to claim 1, the screen being a rear projection screen, and theoptical unit directly focuses the image light emitted from the spatiallight modulation devices onto the screen.
 3. The projector according toclaim 1, the optical unit having an optical axis bent on a verticallyextending plane orthogonal to the screen.
 4. The projector according toclaim 3, the illumination device disposed such that the optical axis ofa lamp serving as a light source to generate illumination light lieshorizontally.
 5. The projector according to claim 1, an exit-sideoptical axis of the projection optical system being orthogonalized to asurface of the screen extending along the central part of the screen. 6.The projector according to claim 1, further comprising: a colormodulation device including the spatial light modulation devices forcorresponding colors, each device being illuminated with correspondingillumination light emitted from the illumination device; and alight-separation modulation device which includes a light-synthesizingmember to synthesize corresponding kinds of color image light emittedfrom the color modulation device and which emits the synthesized imagelight, the projection optical system projecting the image synthesizedwith the light-synthesizing member onto the screen.